Just talked to my brother-in-law who lives in Livingston, Texas. He said he was out in his front yard with his grandson watching the shuttle fly over. He saw the explosion... he is freaking!! He swears there was a plane in the air, too. Is that possible? It isn't too far from Houston International, so I suppose it is nothing.
It is highly unlikely any plane was up there at 207,000 feet. Commercial aircraft fly at roughly 35-42,000 feet. Only military aircraft would fly at 200,000 feet and even then it would be on a test basis only, something like and X-Plane, unless it was the Aurora. The Blackbird used to travel with a top ceiling of around 100,000 feet by press reports. We don't truly know anything concrete about an Aurora.
It might look like a plane was up there, but it would likely be at least 150,000 feet lower, and simply appear like it was next to the shuttle.